The present invention relates to improvements in axisymmetric nozzles of variable geometry and orientation of the flow which nozzles are intended for gas turbine engines, especially for use in aviation.
Axisymmetric nozzles of variable geometry are known which are capable of realizing three functions, namely: regulating a throat area A8 in accordance with a given law; symmetrically varying an exit area with respect to an immobilized throat area; and A9 vectoring thrust through the nozzle in 360 degrees.
The axisymmetric nozzle which is the subject of Spanish Patent No. 9401114 and corresponding U.S. Pat. No. 5,613,636 provides a fourth function: namely, asymmetrically correcting the exit area during thrust vectoring. The nozzle comprises a convergent zone which defines a throat of variable area and is formed by convergent master petals and by convergent slave petals resting on the adjacent convergent master petals, followed in the direction of the flow of gas by a divergent zone formed of divergent master petals and of divergent slave petals resting on the adjacent divergent master petals and connected to the adjacent divergent master petals by a centering mechanism. The petals of the convergent and divergent zones are distributed circumferentially around the longitudinal axis of the engine, and every convergent master petal is connected to a corresponding divergent master petal by a tangential cylindrical articulation having an axis perpendicular to the longitudinal axis of the engine. Each petal of the divergent zone is divided into two segments, an upstream segment and a downstream segment, attached to each other by cylindrical articulations having an axis perpendicular to the tangential cylindrical articulation between the convergent master petal and divergent master petal.
The nozzle further comprises control means for adjusting the throat area and vectoring the thrust, comprising an inner ring, an intermediate ring, and an outer ring, which rings are concentric with respect to each other and to the longitudinal axis of the engine. A plurality of linear actuators are also provided, each having an upstream end and a downstream end. A mechanism for regulating the throat area is also provided, the convergent master petals being attached to the inner ring by tangential cylindrical articulations having axes perpendicular to the longitudinal axis of the engine. The linear actuators are connected articulately at their upstream ends to a fixed structure of the engine, the linear actuator of one part of said plurality of linear actuators having its downstream end attached to spherical articulations of the outer ring and the linear actuator of the other part of each of said plurality of linear actuators having its downstream end connected to spherical articulations of the intermediate ring. Each of the rings is connected independently to the fixed structure of the engine by support means which does not interconnect the rings and maintains each ring fixed laterally.
The nozzle also comprises a set of two-hinged bars, one for each divergent master petal, which interconnect the downstream segments of the divergent master petals with the outer ring. The vectoring, in 360 degrees, of thrust in the divergent zone is obtained by inclination of the outer ring with a center of swing located on the longitudinal axis of the engine through the set of two-hinged bars.
Significantly, the outer ring includes two outer ring segments which are mutually articulated by a pair of cylindrical articulations which make it possible to vary symmetrically the exit area with respect to an immobilized throat area by simultaneously swinging the two outer ring segments in opposite directions, and, during vectoring of the flow of gas, by independently swinging one of the two outer ring segments to correct the exit area asymmetrically while the other outer ring segment remains immobilized.
An axisymmetric nozzle of variable geometry and orientation of flow having the outer ring configuration described above provides several advantages including, without limitation, the following:
1. By vectoring the divergent petals in individual groups, separations of the inner stream of the flow can be avoided which would otherwise take place with large angles of average orientation of the flow and low pressure conditions, which conditions are typical during aircraft landing. In order to avoid said separation, there is obtained a better coefficient of thrust without loss of effectiveness of orientation of the flow, since the energy dissipated upon generating the recirculation is utilized in thrust. Furthermore, the processes of separating fluid streams result in inherent instabilities of not very high frequency which, in a limit case, could be coupled with the frequency itself of the system. PA1 2. If the geometrical vectoring of part of the petals is reduced, the area of oriented flow experienced by the stream outside the aircraft is also reduced. As a result, separations of the outer stream associated with the orientation of the flow are of less intensity. Therefore, the instabilities of such stream decrease, including the overall drag on the aircraft. PA1 3. In an aircraft landing approach, the exit area of the nozzle is vectored downward. Upon decreasing the vectoring of the petals closest to the ground, there is a greater clearance between such petals and the ground in the rear part of the aircraft for the same angle of attack. This makes it possible to land the aircraft with a larger angle of attack and therefore with greater lift or, equivalently, with less speed.
In said Spanish Patent No. 9401114, two embodiments of a four-function nozzle described are described and claimed. U.S. Pat. No. 5,613,636, which corresponds to Spanish Patent No. 9401114, is hereby incorporated herein by reference.
In the first of the embodiments, called a single control system, the inner and intermediate rings and the inter-articulated outer ring segments are interconnected by two pairs of spindles, one pair perpendicular to the other pair. One of the pairs of spindles connects the intermediate ring to the inner ring, and the other pair of spindles connects the intermediate ring to the articulated ends of the outer ring segments, so as to constitute a single control system in combination with the plurality of linear actuators and the mechanism for regulating the throat area. Regulation of the area of the throat is obtained by an axial displacement of the assembly of rings and outer ring segments, and symmetric variation of the exit area with respect to an immobilized throat area is obtained by simultaneously swinging the two outer ring segments in opposite directions. Thrust vectoring is obtained by simultaneously swinging the two outer ring segments in the same direction with the centers of swing on the longitudinal axis of the engine, and asymmetric correction of the exit area during the vectoring of the flow of gas is obtained by independently swinging one of the two outer ring segments while the other outer ring segment remains stationary.
In the second of the embodiments, corresponding to the general case known as a two-control system, the inner and the intermediate rings and the interarticulated two outer ring segments are not connected to each other and constitute, in combination with the plurality of linear actuators and the throat area regulating mechanism, two control systems. The throat area is regulated by axial displacement of only the intermediate ring, and symmetric variation of the exit area with respect to an immobilized throat area is obtained by simultaneously swinging the two outer ring segments in opposite directions. Thrust vectoring is obtained by simultaneously swinging the two outer ring segments in the same direction with a single center of swing on the longitudinal axis of the engine, and asymmetric correction of the exit area during vectoring of the flow is obtained by independently swinging one of the two outer ring segments while the other outer ring segment remains stationary.
In this general case, the second embodiment with two control systems has the advantage, in addition to those mentioned, of a spherical configuration of the inner part of the fairing of the nozzle around the outer ring, since the two outer ring segments have a single point of swing.
The axisymmetric nozzles of variable geometry and orientation of the thrust in 360 degrees are optimum when applied to a gas turbine for aircraft having a single engine or a single jet. However, in the case of aircraft equipped with two engines or twin jets, when the two engines are very close to each other, there are difficulties in orienting the flow in 360 degrees.
A twin jet equipped with nozzles of double symmetry (or 2-D nozzles) has, in theory, properties of maneuverability which are very close to those exhibited by a single engine jet equipped with nozzle which vectors the thrust in 360 degrees. Although a 2-D nozzle vectors the thrust in a single plane which is the plane of pitch of the aircraft, the presence of two 2-D nozzles makes it possible, after an initial maneuver of rotating of the plane about its longitudinal axis by vectoring the thrust of one of the two nozzles or the thrusts of both nozzles simultaneously and in opposite directions, to orient the aircraft by vectoring the thrusts of the two nozzles simultaneously and in the same direction, in any of the directions. It is true that 2-D nozzles have the drawback of greater weight, in addition to great difficulties in the sealing of their components.